Glass chalkboard



Guss CHALKBQARD Filed June 25. 1940 Gttorneg 1 Patented Nov. 24, 1942 UNITED STATE-s PATEN OFFICE Y GLASS cnALxBoAnn Arthur Meli. Greaves-Walker, deceased, late of Toledo, Ohio, by AdelaideM. Greaves-Walker,

executrix, Toledo, Ohio, assignor to The Libbey- Owens-Ford Glass Company, Toledo, Ohio, a

corporation of Ohio Application June 25, 1940, Serial No. 342,255 10 Claims. v(Cl. 35-66) 'I'he present invention relates to chalkboards, such asv are commonly' used in schools, lecture rooms, etc., and has for its aim the provision of such a. -chalkboard having improved qualities of durability, efciency, economy of construction,

and safety.

The chalkboard .concerned includes a facing member comprising a sheet or plate of substantially colorless glass and a backing-thereforcomprising a relatively thin layer of plastic material of the desired color which is visible through said sheet or plate. The front surface of the glass sheet or plate is ground, etched, or otherwise suitably treated or roughened to provide a writing surface which is capable of taking chalk' as well as being readily cleanable.

An important object of the invention is to provide a backing for the glass facing sheet or plate comprising a special type of plastic adhesive material which can be readily and conveniently applied to the glass and which will firmly adhere thereto. Y

`Anotherimportant object of the invention is to provide a backing of plastic adhesive material which is stable, impervious to moisture, unaffected by atmospheric changes, and possessing suicient ductility and elasticity toaccommodate relative expansion and contraction of the glass.

vA further important object of the invention is to provide a backing of plastic adhesive material which will effectually serve its purpose over 'a long period oftime without deterioration and which also serves to greatly increase the resistance of the glass facing sheet or plate to shock or blows as welles acting to retain the pieces of glass against flying or scattering in much the same manner as laminated safety glass in the event the facing sheet .or plate should become accidently broken.

Other objects and advantages of the invention f will become more apparent during the course of the following description, when taken in connection with the accompanying drawing.

In the drawing, wherein like numerals. are' employed to designate like parts throughout the same:

sand-blasted, or roughened in any desired manner to provide a suitable'writing surface.V The invention is not restricted to any particular type of writing surface or method of forming the same so long as it properly takes the chalk and permits the satisfactory erasure thereof. The back surface of the glass sheet or plate is preferably smooth and has applied thereto the backing I2 lcomprising a relatively thin layer of a special .type of plastic adhesive material which adheres iirmly to the glass surface.

The adhesive material forming the backing I2 comprises a plastic compound composedof two basic ingredients, namely, a rubber (latex) paste and a dehydrating powder.l 'I'he concentrated latex paste .and powder are` separately prepared and then mixed together-in predetermined proportions to form a plastic mix of the desired consistency. The dehydrating powder is in -the form of a self-setting cementwhich sets up upon absorption of the -water from "the latex paste.

The consistency of the adhesive is dependent also ordinarily contain other solid materials 'A amounting to approximately 1.5%. 'I'hese solids,

other than the dryl rubber, which constitute the l1.5% are causticalkali as well as naturally occurring proteins which are always found in latex.

Fig. 1 is across sectional view of Aone form of chalkboard embodying the present invention:

Figs. 2, 3, and 4 are similar views showing alternate forms of chalkboards also embodying the invention; and f Fig. 5 is a cross sectional view of one type of apparatus which may be employed for applying the adhesive backing material to the glass facing sheet'or plate.

With reference now to thedrawing and 'particularly to Fig. 1, there is shown a chalkboard including a facing member I0 comprising a sheet or plate of'substantially colorless glass and having the front surface H thereof ground, etched,

The proportions of these ingredients are approximately in the ratio of 0.8%' protein material to 0.7% of caustic alkali calculated as potassium hydroxide. 'Ihe balance of the paste consists of vwater containing arelatively small amount of ammonia which may be approximately 0.05%.

summarizing and by way of example, this paste comprises the following ingredients in the approximate proportions given:

- v Per cent Dry rubber 68.45

Water 30. Ammnnia 0.0 5 Natural proteins'. 0.8 Caustic alkali.(KOI-I) 0.7

'I'he powder consists almost entirely-of a high alumina cement that sets by hydration. To this high alumina cement are added suitable and variable amounts 'of sulfur or other vulcanizing agents such as selenium, etc. Also, to the powder is added suitable accelerators capable of bringing -v about vulcanization without the application of heat such as Butyl Zirnate, zinc butyl xanthate, etc. It is likewise desirable to add to the powder in variable proportions, suitable antioxidants such as Age-rite White, phenyl beta naphthylamine, indanyl resorcinol (sold in the trade as RR5), etc.

More particularly, the powder is composed of inorganic and organic materials, with the inorganicmaterial comprised approximately 98% of the powder. An analysis of one form of powder used by me with excellent results in conjunction with the concentrated latex paste described above shows the inorganic material to consist of Per cent A. Powdered sulfur 1.0 B. High alumina cement 97.0

. Silica (S102) 4.92

' Chemical com- Iron oxide (Fe203) 18.2

position of Alumina (A12Oa) 39.17

typical high Calcium oxide (CaO) 36.03

alumina ce- Magnesia (MgO) 1.54 ment: Sulfuric anhydride The organic constituents of the powder, which comprise an'accelerator and an antioxidant, con stitute substantially 2% of the powder and should be present in approximately the following pro- Per cent High -alumina cement, the analysis of which is given above 97.0 Sulfur 1.0 Accelerator (Butyl Zimate) .5 Antioxidant (Agerite White) 1.5

The adhesive material above described is a lself-setting material and loses its ability to flow freelyin about forty-five minutes, so that the concentrated latex paste and dehydrating powder should not be mixed with one another until it is desired to make use of the material. The adhesive material, however, does not develop an initial set until about four hours old, and good strength or bond is ordinarily developed by the seventh day. Curing of the material, however, continues until about the fourteenth day when maximum strength has developed.

In preparing the adhesive material, it is preferable that the powder be mixed into the paste with a slow. uniform motion that tends to crush any powder lumps. This may be done either in a hand operated mixer or a power driven mixer. Likewise, the mixing of the paste and powder may be carried out ina vacuum to rid the mix of entrapped air. After the paste and powder have been suitably mixed together the material is ready for use.

In carrying out the'invention, a predetermined amount of the powder and paste are first mixed together to give a mixture of the desired consistency. The mix can of course be varied as preferred but it is suggested that't'iparts powder and 5 parts paste by weight will give a mixture of normal consistency. The mixture is then This accelerator is sold in the trade under the name of But l Zimate.

n Th s antioxidant is-sold in the trade under the name 0f Age-rite Vllitef adapted to be applied in a uniform layer to the back surface of the glass facing sheet-or plate I0 and while the adhesive may be sprayed upon or otherwise applied to the glass it is preferred that it be spread or iiowed thereon in the manner illustrated in Fig. 5. As therein shown, the glass facing sheet I0 to be coated is laid horizontally upon a suitable support I3 with the front or writing surface II of said sheet facing downwardly. The numeral I4 designates in its entirety the apparatus used for flowing or spreading a mass of the plastic adhesive material I 5 above described upon the back surface of the glass sheet in the form of the relatively thin film or layer I2.

The spreading apparatus Il comprises a substantially rectangular container including opposite end Walls I6 having vertical rear edges con-4 .to said edges by screws or the like 2l provided with wing nuts 2l. Carried by the cross member I3 is a metal plate 22 having its lower end directed forwardly to provide a substantially horizontal flange or lip 23 whichis spaced above the glass sheet I0 and cooperates therewith to form an outlet of the desired width through which the adhesive material I5 flows. The cross member I9 is provided with slots 2l through which screws 20 are passed so that upon loosening of the screws the cross member can be moved' vertically to vary the distance between the flange 23 and glass sheet I0 to increase or decrease the thickness of the llayer of adhesive material I2 applied to the glass.

In practice, the glass facing sheet I0 is rst laid upon 'the support I3 and the spreading apparatus Il positioned thereover in such a manner that the end walls I6 thereof ride along on top of said support. A supply of the adhesivel sheet to the opposite end thereof. When this is done, the adhesive will ilow through the outlet beneath the flange 23 and be spread thereby upon the glass sheet in the form of a film or layer of uniformthickness. The pressure of the flange 23 upon the layer of adhesive I2 serves to force the adhesive firmly against the glass to improve theadhesion therebetween. As above stated, the adhesive material herein provided is a self-setting material so that after application thereof to the glass it is simply necessary to permit it to set whereupon the chalkboard is ready for use.

By means of the spreading apparatus I4 a uniform layer or film I2 of the adhesive material can be applied to the glass facing sheet or plate to give a uniform color when viewed through .the glass. IZlfhe chalkboard herein provided may be of any preferred color such as, for example, black, green, red, white, grey, etc.; this being accomplished by rendering `the adhesive mate- -rial of the desired color and which is visible -a self-setting plastic mi-x v the color ofadhesive material it is desired to self-setting plastic 1 obtain. v

Although not essential, it may be preferred in some cases tovapply aprotective backing to the layer of adhesive material I2 as shown in Fig. 2, wherein lsuch protective backing is indicated by the numeral 25.A 'I'his backing may consist of waterproof paper, metal foil, etc.

In Fig. 3 is shown how the invention may be applied to a double chalkboard, consisting of two facing sheets or plates o f glass 20 and 21. Applied to the inner surfaces ofthe glass sheets 20 and 21 are the layers of adhesive material 28 and 28, while the outer surfaces 30 and 8i of said sheets are ground, etched, sand-blasted, or

otherwise suitably roughened to give the desired type of writing surface. In this form of chalkboard, the layers of adhesive material 28 and 28 are preferably, although not necessarily, of different colors. The two facing sheets are placed of glass 33 and 3l spaced from one another and mix of the ldesired consistency.

6. A backing for-a glass chalkboard of the character described, comprising an adhesive material including a concentrated latex paste of relatively high concentration having a low protein content and including a stabilizer and preservative, and a powder comprising a high alumina cement that sets by hydration, a vulcanizing agent, an accelerator and an antioxidant, said paste and powder being' mixed together to provide a self-setting plastic mix of the desired consistency.

7. A backing for a glass chalkboard of the character described, comprising an adhesive material mounted in a suitable frame .85. To the back surface of each facing sheet is applied a layer of 'adhesive material 8i covered by a suitable protective backing 81. The front surface 88 of each glass sheet is suitably treated to provide the desired writing surface.

It is to be understood that the form of the invention herewith shown and described is to be taken as the preferred embodiment of the same, and-that various changes in the shape, size and arrangement of parts may be resorted to without departing from the spirit of the invention l or the scope of the subjoin'ed claims.1

What is claimed is:

1. A backing fora glass chalkboard o f the characterdescribed, comprising an adhesive material including a concentrated latex paste and a1 dehydrating powder mixed together to provide of the desired consistency. 2.' A backing for a glass chalkboard of the character described, comprising l an adhesive materialincluding a concentratedlatex paste terial including a concentrated latex paste having a dry rubber content ofjapprozdmately 88% to 70% anda dehydrating powder mixed together to provide a self-setting'plastic mix of the desired consistency.

4. s backing for a gms cnslxboarc'or che.

character described, comprising an adhesive materm' including a concentrated latex omc and including a concentrated latex paste having a dry rubber content of approximately 68% to 70% and a stabilizer and preservative, and a cement powder containing approximately 97% alumina, a vulcanizing agent, an accelerator and an antioxidant, said paste and powder being mixed together as "Butyl Zimate and an antioxidant suchas fAge-rite White, said paste and powder being mixed together to provide a self-setting plastic mix of the desired consistency.

9. A backing for a glass chalkboard of the character described, comprising an adhesive material f including a concentrated latex paste having a dry rubber content of approximately 68% to '10% and a stabilizer and preservative selected from the group consisting of ammonia and caustic all kali,v and a cement powder comprising approximately 97% alumina, a vulcanizing agent such as sulfur, an accelerator such as Butyl Zimate and' an antioxidant such as Age-rite White," said and o dehydration powder containing the 'roia cementv powder that sets by'hydration having an alumina content of approximately 97% mixed together to provide aself-setting plastic mix of the desired consistency.

5. Abackingiorallachalkboard'ofthecharacter described comprising an 'adhesive material includlngaeoncentratedlatexptehavingadry nibbercontentofapproximately 08% to70% and a cement powder having an of character described, comprising an adhesive material including a concentrated latex paste conltaining the following ingredients in the approximate proportions: f

' .5 l Per cent Dry rubber 68.45 .Waterv 30. Ammonia z 0.05 Natural protein's 0.8 Caustic alkali (KOH) 0.7

lowing ingredients in the approximate proportions:

r Per tieni'.A High alumina cement. 97.

ckllwr ("Blltyl Zimate) .5' Anxidant @Age-rite Whlte).. 1,5

' said paste and powder being mixed together to approximateirO'iitmixedtcgethertoprovidea' provide ascii-setting plastic mixof consistency.

ELAIDE M. GRAVES-WALKER,

Executria: of the Estate of Arthur HcK.' Greaves-Walk, Deceased.

the'desired" 

